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Cat Man
Cat Man, Caterpillar Engine Expert
Category: Heavy Equipment
Satisfied Customers: 8822
Experience:  23 Years Caterpillar Engine experience.
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diesel engine rebuild.-

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looking for a very experienced cat diesel engine mechanic. subject: 3406e cat. in-frame engine rebuild.- engine rebuild due to liner failure, causing oil in coolant system & coolant in engine basement.  after rebuild i ran engine 4 cycles at 1200 & 1700 rpm  for axp. 3 hours to flush coolant system due to oil contamination. i removed turbo to r&r water pump to find #3 exhaust port slobbering/ building oil (note #3 only). with turbo removed & turbo oil supply blocked off, i started engine & set to 1500 rpm. i held a clip board axp. 18 inches in front of exhaust manifold to find small amounts of oil spackling on clip board. i checked new cylinder head valve guide seals to find no problem at this time. i have done multiple engine rebuilds over 25 years. i used a snap-on piston ring expander & a cat ring compressor, installation of piston sets to cylinders felt normal to me. what is your professional thought on this matter.-slobbering-                  

Hi. Thanks for using JA! I will try and help you out.


It sounds like you have a problem with the #3 cylinder. If #3 is the only one doing this, you may need to go back into the engine and remove #3 piston and investigate.


But first, does the engine have any miles on it after the inframe?


From your question it sounds like the engine has not been out on it's first run after the inframe. If it has not, I would recommend taking it out and loading the engine. Maybe even letting the driver take it on a short run. There may be a ring seating issue on #3 and it may clear up after the engine has been run under a good load for a while.


Please let me know if you have any more questions.

Customer: replied 6 years ago.

a little more history.- i noticed a small amount of oil seepage at the turbo to exhaust pipe joint apx. 2 1/2 hours into my coolant flush, we have a steep grade hill apx. 1/4 mile long going up to one of our mine pits behind our shop. this is where i was able to load the engine up to 27 psi boost off & on brakes to build a boost psi from 10 to 27 psi. returning to work the next day i started the truck to warm & build air to drive it into the shop, when i was side tracked with an electrical problem from another driver -returning to my eng. rebuild project apx. 1-1/4 hour later (note: eng had been left idling ). removed turbo to r&r water pump & looked at the exhaust ports due to a red flag exhaust joint oil leak to find a little wet around valve stems at # XXXXX cyl port. my exhaust manifold was dry to the touch releaving concerns at this time -after the water pump r&r i started engine with no turbo to charge a/c system due to waiting for a new turbo replacement. at this time my slobber problem came to life (what a drag!). my thought is as yours, give it a good run in under a full 100/500 lb. hwy. load, [state of wa.] if my oil control ring is broken or damaged, do you think i could damage #3 piston set? if my piston skirt breaks away i'm at a big loss. old school pistons, no worries. my run-in time & idle time was twice as long as normal before sending it to work. well this is were i stand, do or die, i'm looking for another professional opinion.

Thanks for the information.


If there is a problem with the rings on #3 piston it could possibly scratch the liner. However, I do not think the engine will suffer a piston skirt failure. That normally occurs when the piston gets overheated. With an oil control ring problem, you should just see oil passing through the cylinder.

If it was me, I would let the unit go out on a loaded run. If there is still a problem after the run with #3 cylinder passing oil, then I would go back into the engine.

Customer: replied 6 years ago.

thank you for the advice .have you seen this symptom often & does a good run in normaly stop this slobbering problem.

You are welcome.


Yes. I have seen this several times in the past. 90% of the time, a good long hard run clears up the oil from the cylinders.

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